The rabbit T cell line, RL-5, which was derived from the B/J inbred strain of rabbits by transformation with the virus Herpes ateles, was used for initial studies concerning the T cell receptor genes of the rabbit. Probes corresponding to the constant region of the murine T cell receptor alpha and beta chain genes were used to screen genomic and cDNA libraries construced from the RL-5 line. The cDNA library yielded two full-length alpha transcripts that were isolated and their sequences determined. It is unexpeced to find two transcripts for a T cell receptor gene in a single clonal cell line. One of the transcripts contained a single base pair deletion in the variable region which placed the remainder of the transcript out-of-phase. The other transcript encoded a complete alpha chain corresponding to a leader sequence, variable region, J region, constant and 3' untranslated regions. Variable region probes from these two transcript were used to probe genomic library and each was found to correspond to multigenic families. Studies on the beta chain transcripts produced by the RL-5 cell line indicated the presence of two transcripts, one 1.3 kb in length, the other approximately 1.0 kb in length. These were sequenced, the larger was found to correspond to a complete T cell beta chain. The other is an incomplete transcript of a beta chain and lacks a variable region. Its sequence is presently under detailed analysis. A probe derived from the variable region of the beta chain dDNA clone detected variable region genes in DNA samples from man, rabbit and pig, but no bands were detected when samples from mouse, rat and hamster were probed under similar conditions. Comparsions of constant region genes from man, mouse and rabbit indicate a high degree of conservation within species and significant, but considerably lower conservation among the species studied. The 3' untranslated regions of the beta genes however, showed conservation among the C beta 1 and C beta 2 regions from the different species. No such identification of beta 1 or beta 2 sequence was possible in comparisons of the constant coding region.